1. Field of the Invention
The present invention relates broadly to textile machines containing drafting arrangements, and, more specifically, to a new and improved autoleveller drafting arrangement and to a method of operating such autoleveller drafting arrangement.
An autoleveller drafting arrangement is a drafting arrangement at which there can be altered in a controlled or regulated manner the draft of the textile material, in order to even out mass fluctuations at a drafted sliver. Such drafting arrangements are frequently used in so-called autolevelling systems in short staple fiber spinning mills, but also can be employed at cards, combing machines and combing preparatory machines in short staple fiber spinning mills. Of course, the same principles are also suitable for use in long staple fiber spinning mills.
2. Background Art
The principles of control and regulation technology have been applied for several decades to autoleveller drafting arrangements. As a result, it was possible to continually improve the quality of the processed slivers to the extent that such quality was governed solely by the uniformity of the mass per unit length of the sliver.
Throughout the same time frame intensive efforts were expended to provide a clear definition of the expression "quality" in respect of uniformity or evenness of the sliver. These efforts resulted in generally accepted testing methods and the attendant availability of suitable testing equipment.
With the aid of the previously employed technology in conjunction with a quality-oriented organization of the spinning mill it is now possible for every spinning mill to avoid or correct most of the relatively coarse errors or defects and to fabricate slivers of good average quality.
Because of the increasing demands imposed upon the quality of the slivers it is necessary to now again further augment this good quality level or performance. However, when attempting to do so one is confronted with a technical area where it is no longer sufficient to merely apply the basic principles of control and regulation technology or the basic principles of statistical quality control in the spinning mill. To achieve a further appreciable increased quality improvement it is now necessary to more fully explore the intimate interaction of the measuring principles, the control and regulation principles, drive systems, drafting forces and textile material properties. In embarking in this direction it is always important to keep in mind the principles of testing for the uniformity of textile slivers which have previously been defined by prevailing predetermined standards.
The control of the sliver quality in the spinning mill is presently extensively undertaken in the laboratory, in other words, so-to-speak "off-line". For this purpose random samples are taken from the processing line, delivered to the laboratory and there checked. The test results are supposed to provide conclusions regarding setting of the machines and to render possible accommodation of the textile material to be processed to the requirements of the final product.
Sufficient time is available in the laboratory, in other words, off-line, to analyze the different information or data, to reach a suitable interpretation of the different results and to draw corresponding conclusions. If attempts are made to utilize such methods "on-line" during normal operation, where interventions should be correctively undertaken in the process based upon the just determined measurement values, it should not be surprising that a real danger exists of reaching faulty or deceptive conclusions. The control and regulation system erroneously interprets the available measurement data and correspondingly incorrectly intervenes in the process.
An attempt at overcoming such a problem has been disclosed in European Patent No. 176,661, Apr. 9, 1986 and the corresponding U.S. Pat. No. 4,653,153, granted Mar. 31, 1987. According to the therein contained proposal brief mass fluctuations of the incoming fiber sliver are evened out by a control which governs the drafting operation. In this connection, two control parameters can be controllably accommodated, namely, the amplification and the time shift or delay. The results of the controlled change in the drafting of the sliver are determined by monitoring the sliver at the outlet or delivery side or end of the drafting arrangement, so that the aforementioned two control parameters can be optimized based upon monitoring of the results. As far as this proposal is concerned from the standpoint of the control and regulation technology, it can not be criticized. However, it is insufficient for achieving the desired improvement in the quality of the sliver because it fails to take into account technological problems, particularly those arising in respect of the measurements and processing of the sliver. Additionally, this proposal is predicated upon the evaluation of momentarily obtained measurement results and intervening in the process, which occurs either immediately or after a simple time delay. The "history" or background of this method is not explored. Comparable concepts are disclosed in Swiss Patent No. 672,928, granted Jan. 15, 1990 and the cognate U.S. Pat. No. 4,819,301, granted Apr. 11, 1989.
A further proposal entailing a "deeper" surveillance of the method is disclosed in European Patent No. 340,756, published Nov. 8, 1989. According to a first embodiment of such proposal, there should be determined threshold values of the signal delivered by the outlet measuring element, and upon exceeding a threshold value there is triggered an alarm and the machine can be shutdown. When that situation occurs the operator is supposed to check the product, in other words, the delivered fiber sliver. As a function of the results derived from such sliver checking operation conclusions should be drawn concerning measurement errors and regulation errors.
A second embodiment of the same proposal contemplates establishing threshold values for the setting or adjustment signal which governs the drafting operation. Here too, upon exceeding a threshold value there is triggered an alarm and the machine is shutdown. In this case, the fiber sliver is checked by an operator. As a function of the checking results conclusions are drawn concerning errors in the inlet measuring system or in the production of the feed material or supply stock, that is, at the production machines upstream of such drafting arrangement.
Monitoring of the measurement signal of the outlet measuring system can furnish certain data regarding faulty or erroneous functions. However, this measure on its own is insufficient to obtain an appreciable improvement in the quality of the sliver. The monitoring of the adjustment signal, as proposed in the aforementioned European Patent No. 340,756, in conjunction with sounding an alarm and shutting down the machine, hardly provides any advantages. Until such time as the operator has checked the sliver the faulty sliver has already been processed (corrected) by the drafting arrangement, so that there is no longer available significant data or information concerning the sliver defect. Since the monitoring operation is set to merely detect a short-time (possibly seldom) fault occurrence or "runaway" situation, the piece or section of the sliver to be examined by the operator no longer contains a corresponding "event", so that again there exists the risk of reaching a deceptive conclusion.
In the commonly assigned, U.S. application Ser. No. 07/566,627, filed Aug. 13, 1990, and entitled "Method and Apparatus for Controlling a Drafting Unit", the disclosure of which is incorporated in its entirety herein by reference, there is disclosed a further developed system which can better take into account, in particular technological measurement problems during determining the high frequency part of the mass fluctuations at the inlet side or end of the drafting arrangement.